When employing an internal combustion engine in an automobile, charging of internal combustion engines by means of a charger driven by the crankshaft is useful when, for reasons of fuel consumption, it is intended to attain a predetermined output goal in stationary as well as mobile operations, which cannot be attained if the internal combustion engine is operated purely under atmospheric pressure. If operated only as an aspirating engine, the size of the internal combustion engine is not sufficient. However, an internal combustion engine of this size has the advantage that it is possible to operate under partial load, which is often used in the course of operating an automobile, to achieve better utilization of fuel, instead of using a larger internal combustion engine which does not require charging to achieve the required full load values.
Most often internal combustion engines for automotive purposes are embodied as reciprocating engines with several cylinders. For reasons of quiet running, the number and placement of the cylinders is selected such that balancing of the forces of inertia is possible. The free forces of inertia are generated by the kinematics of the piston movement which are determined by the geometry of the crank drive. It is known that the number of six cylinders disposed in-line permits complete balancing of the forces of inertia during four-stroke operation. For four-cylinder engines with cylinders disposed in-line, balancing shafts with centrifugal weights are required to balance the free forces of inertia, if vibration-free running of the internal combustion engine is to be achieved.
As already mentioned, for reasons of efficient fuel consumption it is advantageous to utilize for automotive purposes internal combustion engines with a small working volume and to equip them with a charger driven by the crankshaft of the internal combustion engine to achieve the required output goal. As a rule, internal combustion engines with a small working volume also have a smaller number of cylinders than those with a large working volume. Balancing of the free forces of inertia becomes more important with small internal combustion engines with four or fewer cylinders.
Charging of internal combustion engines by means of a positive displacement charger driven by the crankshaft is known from the state of the art. The positive displacement machine can be of the spiral construction type. Such a machine is known from German Patent Publication DE-C3-2 603 462, for example. A charger constructed in accordance with this principle is distinguished by an almost pulsation-free conveying of air or of a gaseous working medium consisting of air and fuel and is particularly suited for charging of internal combustion engines.
The charger is driven by the crankshaft of the internal combustion engine. The charger itself consists of a housing with spiral-shaped conveying chambers disposed therein and of a positive displacement body associated with these conveying chambers, which is fastened on a rotor which can be driven eccentrically in respect to the housing in such a way that during operation each one of its points performs a circular motion, which is limited by the circumferential walls of the positive displacement chamber. An eccentric disk is disposed on the driveshaft for this purpose and has associated counterweights for balancing of the centrifugal forces of the eccentric disk and of the rotor guide by it, generated by the eccentric movement.
A spiral machine is known from European Patent Publication EP 354 342. With this machine, as well as with all other known spiral positive displacement devices wherein a device, for example in the form of a guide shaft operating synchronously with the driveshaft of the rotor, is provided for the translatory guidance of the rotor, balancing of the centrifugal forces generated by the eccentric disk and by the rotor is performed by counterweights fastened on the driveshaft.
As a rule, the charger is driven via a belt drive with a defined transmission ratio in respect to the crankshaft of the internal combustion engine. In the case of a spiral machine, the rpm of the charger are greater by a factor of approximately 1.5 to 2.5 than those of the internal combustion engine.